1. Field of the Invention
The present invention relates to a semiconductor device and a memory device.
The present invention relates to an object, a method, or a manufacturing method. In addition, the present invention relates to a process, a machine, manufacture, or a composition of matter. One embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a memory device, an imaging device, a method for driving them, or a method for manufacturing them. In particular, one embodiment of the present invention relates to a semiconductor device, a display device, or a light-emitting device each including an oxide semiconductor.
In this specification and the like, a semiconductor device generally means a device that can function by utilizing semiconductor characteristics. In some cases, a display device, an electro-optical device, a semiconductor circuit, or an electronic device includes a semiconductor device.
2. Description of the Related Art
Attention has been focused on a technique for forming a transistor using a semiconductor thin film formed over a substrate having an insulating surface (also referred to as thin film transistor (TFT)). Such transistors are applied to a wide range of electronic devices such as an integrated circuit (IC) and an image display device (display device). A semiconductor material typified by silicon is widely known as a material for a semiconductor thin film that can be used for a transistor, and an oxide semiconductor has been attracting attention as well. For example, a technique for manufacturing a transistor using zinc oxide or an In—Ga—Zn oxide semiconductor is disclosed (see Patent Document 1).
The off-state current of a transistor using an oxide semiconductor is extremely low. Patent Documents 2 and 3 each disclose a nonvolatile memory device utilizing the above feature by including an oxide semiconductor transistor. Such a memory device does not have a limit on the number of times of data rewriting and consumes low power.